Discrimination of surface defects based on pulsed magnetic flux leakage

In this paper, the effect of eddy current on pulse magnetic flux leakage (PMFL) signals is considered. The PMFL signals of defects under different excitation voltages, relative permeability of the magnetic core, defect depth and burial depth are simulated, and the overshoot and fluctuation phenomena of the defect signals are found. Based on the phenomena, two methods for discrimination of near surface and deep buried efects are proposed, the overshoot and fluctuation phenomena method and the extreme value of the derivative signals method. Finally, the feasibility of the above methods is verified by experiments.